The Spira 21 uses the unique no-stop screw SPIRAWIND middle shaft technology. It enhances the anti-torsion by 12%, anti-pressure by 9%, anti-crash by 15%, and anti-fatigue by 35%. It can attain the stability and anti-torsion that ordinary products cannot reach . .

The racket structure of oval AERODYNAMIC shape can reduce air resistance and give greater head speed. The Spira 21 is light and with the Square Head Shape the sweet spot is increase by 10%..